This invention is in the field of aqueous film coating of solid forms such as pharmaceutical products, food products, confectionery products, and seeds for agriculture, and is more specifically concerned with providing such coatings based on polydextrose.
Cellulose polymers such as hydroxypropyl nethylcellulose have long been recognized in the art as being suitable for the aqueous film coating of pharmaceutical tablets and the like.
While it is normally possible to produce excellent film coatings with such cellulosic materials, difficulties can sometimes arise with respect to the ability of the resultant film coatings to adhere satisfactorily to the surface to which they are applied. This is especially true when considering tablet substrates such as waxy matrix sustained release products and multi-vitamin products (with which the phenomenon of xe2x80x9cbridgingxe2x80x9d of the coating across debossed legends can be a substantial problem).
It is also desirable to be able to produce film coatings for food and confectionery products which are able to replace the currently used sugar coatings, in order to meet the requirements for low calorie, non-cariogenic (that is, not harmful to teeth) coatings for such products.
While cellulosic polymers can meet these requirements, they tend to produce coatings that have undesirable taste and mouth-feel (that is, they are somewhat bitter and slimy in texture; both undesirable features especially for confectionery products).
Aqueous film coatings based on the polymer polydextrose provide the solution to both the pharmaceutical, and the food and confectionery problems described. Used alone, or in combination with other polymers, polydextrose produces pharmaceutical film coatings that exhibit excellent adhesive qualities, while when used in food and confectionery applications, it can produce coatings with good organoleptic properties that are low calorie and non-cariogenic in nature.
Aqueous film coatings based on the polymer polydextrose are useful on various grains and seeds since such coatings facilitate handling of the grains and seeds. For example, some automatic planting machines do not effectively manipulate seeds that are tiny in size, and coating such seeds with the inventive coating creates a larger volume that is more easily handled by the automatic planting machines. Further, the inventive coating maintains the germinative properties of the seeds.
One characteristic of polydextrose, however, is that it has an extremely low average molecular weight value (for example, peak molecular weight, Mp, is approximately 1230). It is well known that low molecular weight polymers produce extremely weak films. Rowe (xe2x80x9cMolecular Weight Studies on Hydroxypropyl Methylcellulose Phthalatexe2x80x9d Acta-Pharm. Technologica 28 (2), p. 129 1982) has stated that for the purposes of film coating, there exists a CRITICAL MOLECULAR WEIGHT value for polymers such as hydroxypropyl methylcellulose (H.P.M.C.), below which there is a great risk of the coating cracking. For H.P.M.C., he stated that the Mp value, which is indicative of the molecular weight of the main component, is approximately 8.0xc3x97104.
This value for HPMC is significantly greater than the Mp value for polydextrose, which would thus not be expected to produce satisfactory film coatings.
Additionally, Osterwald (xe2x80x9cProperties of Film-Formers and Their Use in Aqueous Systemsxe2x80x9d, Pharm. Res., 1985, p. 15) has stated that for film coating, polymers producing solutions (containing 2% w/w of the polymer in water) having viscosities in the range of 3-15 mPas (milli Pascal seconds) (same as centipoise numerically) ought to be used, and that below this range, the polymer chains shorten to such an extent that the stability of the film is affected (i.e. film strength decreases too much). Two percent aqueous solutions of polydextrose have a viscosity of less than 2 mPas (in fact the value is too low to be differentiated from that of plain water).
Consequently, to those skilled in the art, polydextrose would be considered to produce film coatings that are entirely unsuitable for modern film coating processes; yet we have found it can produce excellent film coatings that in some cases have superior properties to those obtained from more traditional polymers.
Finally, polydextrose can be formulated into a dry-edible film coating composition, shipped to the user and mixed easily into water to form an aqueous coating suspension.
The polydextrose aqueous coating suspension comprises an effective amount of polydextrose, plasticizer, detackifier, and a secondary film former, mixed into water to form an aqueous coating suspension which may be applied to the forms to be coated, as by spraying. Optionally, a colorant may be added to the aqueous coating suspension before the coating step. Also, other polymers, such as maltodextrin and cellulosic, vinylic, and acrylic polymers, may be used in combination with polydextrose. For example, a cellulosic polymer, such as hydroxypropyl methylcellulose, may be substituted for the secondary film former, and the resulting formula is particularly adapted for coating waxy matrix tablets, which are particularly difficult to coat. All ingredients of the coating suspension are edible and suitable for ingestion.
The film former of the coating is polydextrose, or a mixture of polydextrose and one or more other polymers, such as a cellulosic polymer film former.
Also, it may be advantageous to coat with a layer of polydextrose aqueous coating suspension, and then overcoat with a layer of another polymer coating suspension such as a cellulosic film polymer coating suspension.
Other polymers that may be used with polydextrose may be maltodextrin, vinylic polymers, acrylic polymers and cellulosic polymers. The acrylic polymer may be an acrylic latex. The cellulosic film polymer may be hydroxypropyl methylcellulose, hydroxypropyl cellulose, pseudolatex ethylcellulose, or water-soluble cellulose acetate.
The plasticizer may be polyethylene glycol, triacetin, propylene glycol, acetyltriethyl citrate, dibutyl sebacate, or glycerine.
The colorants may be FDandC lakes, DandC lakes, titanium dioxide, or dyes approved for ingestion by the U.S. Federal Drug Administration. Examples of such pigments are listed in Colorcon U.S. Pat. No. 4,543,370 issued Sep. 24, 1985, and incorporated herein by reference.
The detackifier may be lecithin or mineral oil.
The secondary film former may be sodium alginate or propylene glycol alginate.
With some polymer coatings, such as polydextrose/EUDRAGIT formula coatings, an antifoaming agent (such as AEROSOL OT, 75%) and a lubricating aid (such as magnesium stearate) may be added to the formula.
The polydextrose based coating is especially effective in coating tablets and the like having debossed or intaglio logos, trademarks, designs or words thereon since it adheres to the tablet surfaces without bridging and obscuring the debossed or intaglio printing.